How To Customize The Supertip Of An Excel Ribbon

Question

I'm using the Custom UI Editor to customize my Excel ribbon with the following code:

<customUI xmlns="http://schemas.microsoft.com/office/2006/01/customui">
    <ribbon startFromScratch="false">
        <tabs>
            <tab id="customTab" label="MyWorkbookTest">
                <group id="customGroup1" label="Utilities">
                    <button id="customButton1" label="About" imageMso="ResultsPaneAccessibilityMoreInfo" size="large" supertip="View the framework version and status" onAction="ShowAbout" />
                    <button id="customButton2" label="Contact" imageMso="HyperlinkInsert" size="large" supertip="Launch the 'Contact Us' webpage" onAction="ShowContactUs" />
                </group>
            </tab>
        </tabs>
    </ribbon>
</customUI>

Can anyone tell me how to delete the part circled in red coming out automatically?

Result